This invention relates to methods and apparatus for testing integrated circuit packages (IC packages) for leaks.
One type of integrated circuit package which the present invention tests is comprised of a ceramic body and a lid that is sealed to the body to thereby form an enclosed cavity. Lying within this cavity are semiconductor chips, and they are electrically interconnected via conductors which run through and extend from the body. Ideally, the cavity in which the chips lie is airtight, and thus the chips are protected from external contaminants. However, in any large volume manufacturing environment, a certain percentage of the cavities will have a leaky lid seal. Consequently, all of the packages must be tested for leaks.
Conventionally, the packages are tested for leaks as follows. To begin, the package is submerged in a first liquid which has a relatively low boiling temperature. This step is performed to force some of the liquid into the cavity if the lid seal has a gross leak. Thereafter, the package is submerged in a second liquid which is hotter than the boiling temperature of the first liquid. This step is performed in order to vaporize any of the first liquid which may have leaked into the package cavity. Such a vapor will then leak back out of the cavity and produce bubbles in the second liquid, which indicates the package has a gross leak.
If the package produces no bubbles in the second liquid, then it undergoes another test which detects minor leaks. Initially, in this test, the package is placed in a container which is filled with a certain gas. This step is performed in order to let some of the gas seep into the cavity through any minor leak in the lid seal. Thereafter, all of the gas is removed from the container so that the package is then surrounded by a vacuum; and a sensor in the container monitors the vacuum for any trace of the gas leaking from the cavity back into the container.
While the above described testing process does work, it also has some major drawbacks. For example, if the lid has a gross leak, then the first liquid which seeps into the cavity during the test procedure can contaminate the chips. Thus, the package cannot be salvaged after a leak is detected.
Another problem with the above testing process is that separate tests and separate test stations are required to detect gross and minor leaks. Liquids are required in the gross leak test while gas is required in the fine leak test.
Another problem with the above testing process is that it takes a long time to complete. For example, one common practice in the gross leak test is to submerge the package in a liquid at 15 psi for 13 hours. That time can be shortened by increasing the pressure of the liquid; but increasing the pressure raises the risk of overstressing the package and actually causing leaks in the lid seal and/or damaging the conductors in the package that connect to the chip. Similar stresses are induced in the package in the minor leak test when the package is subjected to a vacuum.
Accordingly, a primary object of the invention is to provide an improved method and apparatus for detecting leaks in integrated circuit packages in which all of the above problems are avoided.